1. Field of the Invention
The present invention relates to an automatic gear transmission adapted for use in automotive vehicles, and more particularly to a gear-shift mechanism for the gear transmission.
2. Description of the Prior Art
In recent year, there has been proposed a gear-shift mechanism for a gear transmission of the type which includes a changeover shaft mounted within a housing of the gear transmission for both axial and rotary movements to be axially shifted from a neutral position to a forward or reverse position in selecting operation and to be rotated at its shifted position in shifting operation, a shift-and-select lever fixed to an intermediate portion of the changeover shaft for axial and rotary movement therewith, an interlock member rotatably mounted in place on the changeover shaft and having a pair of interlock arms located at the opposite sides of the shift-and-select lever, detent means for restricting rotary movement of the interlock member and for permitting axial movement of the interlock member, a plurality of fork shafts mounted in parallel within the housing for axial movement in a shift direction perpendicular to the changeover shaft, a plurality of shift forks mounted on the fork shafts to be selectively engaged with each sleeve of a plurality of changeover mechanisms for selectively establishing a plurality of change-speed gear trains in the gear transmission, a plurality of shift heads mounted on the fork shafts to be selectively engaged with the shift-and-select lever at their neutral positions, a first actuator operatively connected to the changeover shaft for effecting rotary movement of the changeover shaft when activated under control of an electric controller, a shift-stroke sensor for detecting the operation of the first actuator, a second actuator operatively connected to the changeover shaft for effecting axial movement of the changeover shaft when activated under control of the electric controller, and a selection-stroke sensor for detecting the operation of the second actuator.
In such a gear transmission as described above, if a failure occurs in any one of the stroke sensors during travel of an automotive vehicle, it becomes impossible for the electric controller to determine whether a desired speed gear train has been correctly established or not. This causes an error in operation of the electric controller. For this reason, it is preferable that the electric controller is designed to stop the vehicle in the occurrence of a failure in any one of the stroke sensors for safety of the driver and to avoid unexpected trouble caused by an error in its operation. On the other hand, it is required to design the gear-shift mechanism in such a manner that the vehicle can be started to drive to a repair shop after stopped under control of the electric controller.
It is, therefore, a primary object of the present invention to provide a gear-shift mechanism capable of starting the vehicle in a safety condition in the occurrence of a failure in any one of the stroke sensors.
According to the present invention, the object is accomplished by providing a gear-shift mechanism for a gear transmission of the type which includes a changeover shaft mounted within a housing of the gear transmission for both axial and rotary movements to be axially shifted from a neutral position to a forward or reverse position in selecting operation and to be rotated at its shifted position in shifting operation, a shift-and-select lever fixed to an intermediate portion of the changeover shaft for axial and rotary movements therewith, an interlock member rotatably mounted in place on the changeover shaft and having a pair of interlock arms located at the opposite sides of the shift-and-select lever, detent means for restricting rotary movement of the interlock member and for permitting axial movement of the interlock member, a plurality of fork shafts mounted in parallel within the housing for axial movement in a shift direction perpendicular to the changeover shaft, a plurality of shift forks mounted on the fork shafts to be selectively engaged with each sleeve of a plurality of changeover mechanisms for selectively establishing a plurality of change-speed gear trains in the gear transmission, a plurality of shift heads mounted on the fork shafts to be selectively engaged with the shift-and-select lever at their neutral positions, a first actuator operatively connected to the changeover shaft for effecting rotary movement of the changeover shaft when activated under control of an electric controller, a shift-stroke sensor for detecting the operation of the first actuator, a second actuator operatively connected to the changeover shaft for effecting axial movement of the changeover shaft when activated under control of the electric controller, and a selection-stroke sensor for detecting the operation of the second actuator, wherein the shift-and-select lever is loaded by resilient means assembled therewith toward an initial position in which the shift-and-select lever is brought into engagement with one of the shift heads for establishing a low speed gear train, and wherein in the occurrence of a failure in at least one of the selection-stroke sensor and the shift-stroke sensor, the second actuator is deactivated under control of the electric controller to permit free movement of the changeover shaft in an axial direction and the first actuator is activated under control of the electric controller to effect rotary movement of the changeover shaft so that the shift-and-select lever is moved to the initial position under the load of the resilient means and brought into engagement with the one of the shift heads to establish the low speed gear train.